An herbal extract which induces immune cells to produce interferon and activates Toll-like receptors and a preparation method thereof are provided. The herbal extract is extracted from an effective amount of raw material including Glycyrrhizae Radix, Bupleuri Radix, Scutellariae Radix, Schisandrae Fructus and Paeoniae Rubra Radix. Glycyrrhizae Radix, Bupleuri Radix, Scutellariae Radix, Schisandrae Fructus and Paeoniae Rubra Radix have a weight ratio of 1-5:1-5:1-5:1-3:1-3.